Abstract

Recently it has been frequently reported arsenic contamination of geologic origin in groundwater. The ironimpregnated granular activated carbon (Fe-GAC) was developed for effective removal of arsenic from groundwater in the study. Fe-GACs were prepared by impregnating iron compounds into a supporting medium (GAC) with 0.05 M iron nitrate solution. The materials were used in arsenic adsorption isotherm tests to know the effect of iron impregnation time, batch kinetic tests to understand the influence of pH, and column tests to evaluate for the preliminary operation of water treatment system. The results showed that the minimum twelve hours of impregnation time were
required for making the Fe-GAC with sufficient iron content for arsenic removal, confirmed by a high arsenic adsorption capacity evaluated in the isotherm tests. Most of the impregnated iron compounds were iron hydroxynitrate (Fe₄(OH)₁₁NO₃·2H₂O) but a small quantity of hematite was also identified in X-ray diffraction(XRD) analysis. The batch isotherms of Fe-GAC for arsenic adsorption were well explained by Langmuir than Freundlich model and the iron contents of Fe-GAC have positive linear correlations on logarithmic plots with Freundlich distribution coefficients (K_F) and Langmuir maximum adsorption capacities (Q_m). The results of kinetic experiments suggested that Fe-GAC had the excellent arsenic adsorption capacities regardless of all pH conditions except for pH 11 and could be used a promising adsorbents for groundwater arsenic removal considering the general groundwater pH range of 6-8. The pseudo-second order model, based on the assumption that the rate-limiting step might be chemisorption, provided the best correlation of the kinetic experimental data and explained the arsenic adsorption system of Fe-GAC. The column test was conducted to evaluate the feasibility of Fe-GAC use and the operation parameters in arsenic groundwater treatment system. The parameters obtained from the column test were the retardation
factor of 482.4 and the distribution coefficient of 581.1 L/mg which were similar values of 511.5-592.5 L/mg acquired from Freundlich batch isotherm model. The results of this study suggested that Fe-GAC could be used as a promising adsorbent of arsenic removal in a small groundwater supply system with water treatment facility.

Keywords groundwater, arsenic, iron-impregnated granular activated carbon, adsorbent, water treatment system